Method and system to determine capture thresholds

ABSTRACT

Computer implemented methods and systems are provided for automatically determining capture thresholds for an implantable medical device equipped for cardiac stimulus pacing using a multi-pole left ventricular (LV) lead. The methods and systems measures a base capture threshold for a base pacing vector utilizing stimulation pulses varied over at least a portion of an outer test range. The base pacing vector is defined by a first LV electrode provided on the LV lead and a second electrode located remote from an LV chamber. The methods and systems designate a secondary pacing vector that includes the first LV electrode and a neighbor LV electrode provided on the LV lead. The methods and systems further define an inner test range having secondary limits based on the base capture threshold, wherein at least one of the limits for the inner test range differs from a corresponding limit for the outer test range. The methods and systems measure a secondary capture threshold associated with the secondary pacing vector utilizing stimulation pulses varied over at least a portion of the inner test range.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/067,054, filed Mar. 10, 2016.

BACKGROUND OF THE INVENTION

Embodiments of the present disclosure generally relate to determiningcapture thresholds, and more particularly to methods and systems toautomatically adjust test ranges based on prior measured capturethresholds.

Implantable stimulation devices or cardiac pacemakers are a class ofcardiac rhythm management devices that provide electrical stimulation inthe form of pacing pulses to selected chambers of the heart. As the termis used herein, a pacemaker is any cardiac rhythm management device witha pacing functionality regardless of any additional functions it mayperform, such as cardioversion/defibrillation.

A pacemaker is comprised of two major components, a pulse generator anda lead. The pulse generator generates the pacing stimulation pulses andincludes the electronic circuitry and the power cell or battery. Thelead, or leads, is implanted within the heart and has electrodes whichelectrically couples the pacemaker to the desired heart chamber(s). Alead may provide both unipolar and bipolar pacing and/or sensingconfigurations. In the unipolar configuration, the pacing pulses aregenerally applied (or responses are sensed) between an electrode carriedby the lead and a case of the pulse generator or an electrode of anotherlead within the heart. In the bipolar configuration, the pacing pulsesare applied (or responses are sensed) between a pair of electrodescarried by the same lead. Recently, pacing systems have been introducedthat stimulate multiple sites in the same chamber, termed multisitestimulation systems or multi-purpose pacing systems.

When the patient's own intrinsic rhythm fails, pacemakers can deliverpacing pulses to a heart chamber to induce a depolarization of thatchamber, which is followed by a mechanical contraction of that chamber.Pacemakers further include sensing circuits that sense cardiac activityfor the detection of intrinsic cardiac events such as intrinsic atrialdepolarizations (detectable as P waves) and intrinsic ventriculardepolarizations (detectable as R waves). By monitoring cardiac activity,the pacemaker circuits are able to determine the intrinsic rhythm of theheart and provide stimulation pacing pulses that force atrial and/orventricular depolarizations at appropriate times in the cardiac cyclewhen required to help stabilize the electrical rhythm of the heart. Thistherapy is referred to as cardiac resynchronization therapy (CRT).

Recently, multi-point pacing (MPP) technology has enabled pacing at leftventricular (LV) sites to improve synchrony in cardiac resynchronizationtherapy (CRT) patients. Improvements in synchrony and improvedhemodynamic response have been shown to depend on the MPP configuration.In the past, MPP configurations have been selected based on reducingpacing capture thresholds, avoiding atrial and phrenic nerve capture,and maximizing anatomical distance between LV pacing sites.

Further, quadrupole or multi-electrode LV leads have been found toafford more LV pacing vector options. Different pacing vector optionsmay be chosen in order to avoid high capture thresholds and phrenicnerve stimulation and to select a preferred LV pacing site. Today,various device-based algorithms exist for automatically determining theLV pacing thresholds based on changes in evoked responses. However,existing automatic threshold determining techniques utilize an extendedperiod of time, relative to conventional bipolar leads, when determiningcapture thresholds for a large number of LV pacing vectors (e.g. 10 ormore vectors).

A need remains for improved methods and systems that automaticallyidentify capture thresholds and reduce the time utilized for identifyingavailable LV pacing vectors.

SUMMARY

In accordance with embodiments herein a computer implemented method isprovided for automatically determining capture thresholds for animplantable medical device equipped for cardiac stimulus pacing using amulti-pole left ventricular (LV) lead. The method comprises, undercontrol of one or more processors configured with program instructions,measuring a base capture threshold for a base pacing vector utilizingstimulation pulses varied over at least a portion of an outer testrange. The base pacing vector is defined by a first LV electrodeprovided on the LV lead and a second electrode located remote from an LVchamber. The method designates a secondary pacing vector that includesthe first LV electrode and a neighbor LV electrode provided on the LVlead. The method further defines an inner test range having secondarylimits based on the base capture threshold, wherein at least one of thelimits for the inner test range differs from a corresponding limit forthe outer test range. The method measures a secondary capture thresholdassociated with the secondary pacing vector utilizing stimulation pulsesvaried over at least a portion of the inner test range.

Optionally, the measuring of the base capture threshold includesdelivering successive stimulation pulses that have different stimulationamplitudes starting at an upper limit of the outer test range anddecreasing by predetermined amounts. The measuring of the secondarycapture threshold includes delivering one or more pacing pulses havingstimulation amplitudes varying over the inner test range. One or morepacing pulses begins with an initial stimulation amplitude having avoltage that is lower than a voltage of an initial stimulation amplitudeassociated with the outer test range used to measure the base capturethreshold.

Optionally, the measuring of the base and secondary capture thresholdsbegin at first and second outer voltages corresponding to one of thelimits of the outer and inner test ranges, respectively. The first andsecond outer voltages may differ from one another by an amount based ona correlation map. The second outer voltage is set to equal apredetermined multiple of the first outer voltage or to equal adifference between the first outer voltage and a predetermined offset.

The method further comprises setting the first LV electrode, utilized todefine the base and secondary pacing vectors, as a cathode electrode andsetting the second electrode and the neighboring LV electrode as anodeelectrodes. The method may set the base pacing vector to represent aunipolar pacing configuration, such that the base capture thresholdrepresents a unipolar capture threshold, and may set the secondarypacing vector to represent a bipolar pacing configuration, such that thesecondary capture threshold represents a bipolar capture threshold.

Optionally, measuring the secondary capture threshold includes defininga select cut off limit for the inner test range and beginningmeasurements for the secondary capture threshold at the select cut offlimit, when loss of capture is detected at the select cut off limit,proceeding to a next pacing vector without determining a capturethreshold associated with the secondary capture vector. The measuring,designating and defining operations are repeated for multiple secondarypacing vectors associated with the base pacing vector. The measuring,designating and defining operations are repeated for multiple basepacing vectors, each of which has at least one secondary pacing vector.Optionally, at least one of measuring the base capture threshold ormeasuring the secondary capture threshold may comprise performing aquick scan such that, when loss of capture is detected, the processproceeds to a next pacing vector.

In accordance with embodiments herein a system is provided forautomatically determining capture thresholds for an implantable medicaldevice equipped for cardiac stimulus pacing using a multi-pole leftventricular (LV) lead. The system comprises at least one processor and amemory coupled to the at least one processor, wherein the memory storesprogram instructions. The program instructions are executable by the atleast one processor. The system measures a base capture threshold for abase pacing vector utilizing stimulation pulses varied over at least aportion of an outer test range, the base pacing vector defined by afirst LV electrode provided on the LV lead and a secondary electrodelocated remote from an LV chamber. The system designates a secondarypacing vector that includes the first LV electrode and a neighbor LVelectrode provided on the LV lead. The system further comprises adefined inner test range having limits based on the base capturethreshold, wherein at least one of the limits for the inner test rangediffers from a corresponding limit for the outer test range. The systemmeasures a secondary capture threshold associated with the secondarypacing vector utilizing stimulation pulses varied over at least aportion of the inner test range.

Optionally, the system comprises a pulse generator that delivers, inconnection with measuring the base capture threshold, successivestimulation pulses that have different stimulation amplitudes startingat an upper limit of the outer test range and decreasing bypredetermined amounts. The system further comprises a pulse generatorthat delivers, in connection with measuring the secondary capturethreshold, one or more pacing pulses having stimulation amplitudes thatvary over the inner test range.

Optionally, the pulse generator delivers one or more pacing pulsesbeginning with an initial stimulation amplitude having a voltage that islower than a voltage of an initial stimulation amplitude associated withthe outer test range used to measure the base capture threshold. Thepulse generator, in connection with measuring the base and secondarycapture thresholds, begins at first and second outer voltagescorresponding to one of the limits of the outer and inner test ranges,respectively, the first and second outer voltages differing from oneanother. Optionally, a correlation map may define a relation between thebase capture threshold and at least one outer limit of the Inner testrange.

Optionally, the second outer voltage is set to equal a predeterminedmultiple of the first outer voltage or to equal a difference between thefirst outer voltage and a predetermined offset. The system may furthercomprise a pulse generator and a switch, the switch defining the baseand secondary pacing vectors by connecting the pulse generator to thefirst LV electrode in a manner that sets the first LV electrode as acathode electrode, the switch connecting the second electrode and theneighbor LV electrode as anode electrodes. The system may furthercomprise a switch that sets the base pacing vector to represent aunipolar pacing configuration and that sets the secondary pacing vectorto represent a bipolar pacing configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an implantable medical device (IMD) in electricalcommunication with multiple leads implanted into a patient's heart fordelivering multi-chamber stimulation and sensing cardiac activityaccording to an embodiment.

FIG. 2A illustrates a simplified block diagram of internal components ofthe IMD (e.g., IMD) according to an embodiment.

FIG. 28 illustrates examples of correlation maps that may be stored inthe memory in accordance with embodiments herein.

FIG. 3A illustrates LV capture thresholds collected for patientsutilizing a quadrupole LV lead and a lead having an RV coil electrode inthe right ventricle in accordance with embodiments herein.

FIG. 3B illustrates a collection of correlation plots that map capturethresholds associated with different combinations of pacing vectorsrelative to one another in accordance with embodiments herein.

FIG. 3C illustrates a series of histograms plotting differences betweencapture thresholds for the same patient data used to derive the graphsand plots in FIGS. 3A and 3B in accordance with embodiments herein.

FIG. 4A illustrates a method for automatically determining capturethresholds for various pacing vectors in accordance with embodimentsherein.

FIG. 4B illustrates an example of the operations performed to measurethe capture threshold associated with a base pacing vector in accordancewith embodiments herein.

FIG. 4C illustrates an example of the operations performed to measurethe capture threshold associated with a secondary pacing vector inaccordance with embodiments herein.

FIG. 4D illustrates a “quick scan” or “abbreviated scan” method forautomatically determining capture thresholds for various pacing vectorsin accordance with embodiments herein.

FIG. 5 illustrates a functional block diagram of an external device thatis operated in accordance with the processes described herein.

DETAILED DESCRIPTION

The systems described herein can include or represent hardware andassociated instructions (e.g., software stored on a tangible andnon-transitory computer readable storage medium, such as a computer harddrive, ROM, RAM, or the like) that perform the operations describedherein. The hardware may include electronic circuits that include and/orare connected to one or more logic-based devices, such asmicroprocessors, processors, controllers, or the like (collectively“processors”). These devices may be off-the-shelf devices that performthe operations described herein from the instructions described above.Additionally or alternatively, one or more of these devices may behard-wired with logic circuits to perform these operations.

The foregoing summary, as well as the following detailed description ofcertain embodiments, will be better understood when read in conjunctionwith the appended drawings. To the extent that the FIGS. illustratediagrams of the functional blocks of various embodiments, the functionalblocks are not necessarily indicative of the division between hardwareand circuitry. Thus, for example, one or more of the functional blocks(e.g., processors or memories) may be implemented in a single piece ofhardware (e.g., a general purpose signal processor, microcontroller,random access memory, hard disk, and/or the like). Similarly, theprograms may be standalone programs, may be incorporated as subroutinesin an operating system, may be functions in an installed imagingsoftware package, and the like. Furthermore, to the extent that theFIGS. illustrate flow diagrams of processes of various embodiments, theoperations may be described by adding, rearranging, combining, oromitting the illustrated operations without departing from the scope ofthe processes as described herein. It should be understood that thevarious embodiments are not limited to the arrangements andinstrumentality shown in the drawings.

One or more embodiments generally relate to implantable medical devicesand systems such as pacemakers and implantablecardioverter-defibrillators (ICDs). One or more embodiments relate, inparticular, to such devices and systems that include a multi-pole LVlead capable of pacing from one or more electrodes along the multi-polelead, and methods for use therewith. New multipolar left ventricular(LV) leads have been developed for implantable medical devices (IMDs)that include multiple electrodes for placement in the LV chamber. Forexample, St. Jude Medical, Inc. (headquartered in St. Paul, Minn.) hasdeveloped the Quartet™ LV pacing lead, which includes four pacingelectrodes on the LV lead.

System Overview

In accordance with embodiments herein, methods and systems utilizeinformation determined utilizing select or base pacing vectors inconnection with determining test ranges to search for capture thresholdsthat may be exhibited by other “secondary” pacing vectors. As notedherein, certain combinations of pacing vectors exhibit relations betweencapture thresholds. When the capture threshold for one pacing vector ismeasured, it can be useful in predicting a narrow test range to searchfor the capture threshold of a related pacing vector. The relations areindicated herein as base and secondary.

In accordance with embodiments herein, methods and systems are providedthat utilize a predetermined relation (as maintained in a correlationmap) between capture thresholds for different pacing vectors to narrowcandidate test ranges (also referred to as secondary or inner testranges) to utilize when searching for capture thresholds associated withsecondary pacing vectors. The limits of the secondary or inner testranges are determined based on the capture threshold measured for one ormore base pacing vectors. The methods and systems measure the capturethreshold(s) for one or more base pacing vectors. The measured capturethresholds are applied to a correlation map to obtain limits of theInner test range to be utilized in connection with measuring the capturethresholds for secondary pacing vectors. The inner test range representsa range over which one or more stimulation parameters are varied whilesearching for a capture threshold for a particular pacing vector. Theinner test range may include a limit for an upper or lower end of therange that corresponds to an upper or lower limit of the base test rangeused in connection with determining the base capture threshold.

The inner test range is narrower than the original “outer” test rangeused when searching for the capture threshold of a base pacing vector.The inner test range may fall entirely within the outer test range ormay only partially overlap the outer test range.

In accordance with embodiments herein, multiple different base pacingvectors are tested to identify associated base capture thresholds. Oneor more of the base pacing vectors have correlation maps associated withone or more secondary pacing vectors. The correlation maps enable themethods and systems to identify a narrow inner test range with a subsetof test points to be measured in search of the capture threshold for thesecondary pacing vector(s).

FIG. 1 illustrates an implantable medical device (IMD) 100 in electricalcommunication with multiple leads implanted into a patient's heart 105for delivering multi-chamber stimulation and sensing cardiac activityaccording to an embodiment. The IMD 100 may be a dual-chamberstimulation device, including a IMD, capable of treating both fast andslow arrhythmias with stimulation therapy, including cardioversion,defibrillation, and pacing stimulation, including CRT. Optionally, theIMD 100 may be configured for single site or multi-site left ventricular(MSLV) pacing, which provides pacing pulses at more than one site withinthe LV chamber each pacing cycle. The IMD 100 may be referred to hereinas IMD 100. To provide atrial chamber pacing stimulation and sensing,IMD 100 is shown in electrical communication with a heart 105 by way ofa left atrial (LA) lead 120 having an atrial tip electrode 122 and anatrial ring electrode 123 implanted in the atrial appendage 113. IMD 100is also in electrical communication with the heart 105 by way of a rightventricular (RV) lead 130 having, in this embodiment, a ventricular tipelectrode 132, an RV ring electrode 134, an RV coil electrode 136, and asuperior vena cava (SVC) coil electrode 138. The RV lead 130 istransvenously inserted into the heart 105 so as to place the RV coilelectrode 136 in the RV apex, and the SVC coil electrode 138 in thesuperior vena cava. Accordingly, the RV lead 130 is capable of receivingcardiac signals and delivering stimulation in the form of pacing andshock therapy to the right ventricle 114 (also referred to as the RVchamber).

To sense left atrial and ventricular cardiac signals and to provide leftventricle 116 (e.g., left chamber) pacing therapy, IMD 100 is coupled toa multi-pole LV lead 124 designed for placement in various locationssuch as the “CS region”, the epicardial space, etc. As used herein, thephrase “CS region” refers to the venous vasculature of the leftventricle, including any portion of the coronary sinus (CS), greatcardiac vein, left marginal vein, left posterior ventricular vein,middle cardiac vein, and/or small cardiac vein or any other cardiac veinaccessible by the coronary sinus. In an embodiment, an LV lead 124 isdesigned to receive atrial and ventricular cardiac signals and todeliver left ventricular pacing therapy using a set of multiple LVelectrodes 126 that includes electrodes 126 ₁, 126 ₂, 126 ₃, and 126 ₄(thereby providing a multipolar or multi-pole lead). The LV lead 124also may deliver left atrial pacing therapy using at least an LA ringelectrode 127 and shocking therapy using at least an LA coil electrode128. In alternate embodiments, the LV lead 124 includes the LVelectrodes 126 ₁, 126 ₂, 126 ₃, and 126 ₄, but does not include the LAelectrodes 127 and 128. The LV lead 124 may be, for example, theQuartet™ LV pacing lead developed by St. Jude Medical Inc.(headquartered in St. Paul, Minn.), which includes four pacingelectrodes on the LV lead. Although three leads 120, 124, and 130 areshown in FIG. 1, fewer or additional leads with various numbers ofpacing, sensing, and/or shocking electrodes may optionally be used. Forexample, the LV lead 124 may have more or less than four LV electrodes126.

When selecting a target venous branch for the LV lead 124, severalfactors may be taken into account. For example, it may be desirable tomaximize the LV mass that may be captured by the LV lead 124.Accordingly, to maximize LV mass exposure, certain venous branches maybe preferred for positioning the LV lead 124. Further, a diameter andtrajectory of the venous branch is also considered to ensure that thevenous branch will support chronic stability of an LV lead 124. Passivefixation of the LV lead 124 may be established through the anatomy ofthe host venous branch which causes the LV lead 124 to extend the distalportion thereof in a manner that differs from the LV lead's preformedshape. Optionally, additional factors to be considered when placing theLV lead 124 may include reducing myocardial capture thresholds, avoidingatrial and phrenic nerve stimulation and the like. After the LV lead 124is positioned, the LV pacing vectors may be selected.

The LV electrode 126 ₁ (also referred to as P4) is shown as being themost “distal” LV electrode with reference to how far the electrode isfrom the left atrium 118. The LV electrode 126 ₄ (also referred to asD1) is shown as being the most “proximal” LV electrode 126 to the leftatrium 118. The LV electrodes 126 ₂ and 126 ₃ are shown as being“middle” LV electrodes (also referred to as M3 and M2), between thedistal and proximal LV electrodes 125 ₁ and 126 ₄, respectively.Accordingly, so as to more aptly describe their relative locations, theLV electrodes 126 ₁, 126 ₂, 126 ₃, and 126 ₄ may be referred torespectively as electrodes D1, M2, M3, and P4 (where “D” stands for“distal”, “M” stands for “middle”, and “P” stands from “proximal”, andthe numbers are arranged from most distal to most proximal, as shown inFIG. 1). Optionally, more or fewer LV electrodes may be provided on thelead 124 than the four LV electrodes D1, M2, M3, and P4.

The LV electrodes 126 are configured such that each electrode may beutilized to deliver pacing pulses and/or sense pacing pulses (e.g.,monitor the response of the LV tissue to a pacing pulse). In a pacingvector or a sensing vector, each LV electrode 126 may be controlled tofunction as a cathode (negative electrode). Pacing pulses may bedirectionally provided between electrodes to define a pacing vector. Ina pacing vector, a generated pulse is applied to the surroundingmyocardial tissue through the cathode. The electrodes that define thepacing vectors may be electrodes in the heart 105 or located externallyto the heart 105 (e.g., on a housing/case device 140). For example, thehousing/case 140 may be referred to as the CAN 140 and function as ananode in unipolar pacing and/or sensing vectors. The RV coil 136 mayalso function as an anode in unipolar pacing and/or sensing vectors. TheLV electrodes 126 may be used to provide various different vectors. Someof the vectors are intraventricular LV vectors (e.g., vectors betweentwo of the LV electrodes 126), while other vectors are interventricularvectors (e.g. vectors between an LV electrode 126 and the RV coil 136 oranother electrode remote from the left ventricle 116). Below is a listof exemplary bipolar sensing vectors with LV cathodes that may be usedfor sensing using the LV electrodes D1, M2, M3, and P4 and the RV coil136. In the following list, the electrode to the left of the arrow isassumed to be the cathode, and the electrode to the right of the arrowis assumed to be the anode.

D1→RV coil

M2→RV coil

M3→RV coil

P4→RV coil

D1→M2

D1→P4

M2→P4

M3→M2

M3→P4

P4→M2

It is recognized that various other types of leads and IMDs may be usedwith various other types of electrodes and combinations of electrodes.The foregoing electrode types/combinations are provided as non-limitingexamples. Further, it is recognized that utilizing an RV coil electrodeas an anode is merely one example. Various other electrodes may beconfigured as the anode electrode. Below is a list of exemplary bipolarpacing vectors with LV cathodes that may be used for pacing using the LVelectrodes D1, M2, M3, and P4 and the RV coil 136. In the followinglist, the electrodes to the left of the arrow are assumed to becathodes, and the electrode to the right of the arrow is assumed to bethe anode.

D1→RV coil (or CAN)+M2→RV coil (or CAN)

M2→RV coil (or CAN)+M3→RV coil (or CAN)

M3→RV coil (or CAN)+M4→coil (or CAN)

M2→RV coil (or CAN)+M3→RV coil (or CAN)+P4→RV coil (or CAN)

D1→RV coil (or CAN)+M2→RV coil (or CAN)+M3→RV coil (or CAN)

It is noted that the preceding list is only a subset of the availablepacing and sensing vectors for use with the IMD 100. Further, whendelivering a series of pacing pulses, one of the above LVEC pacingvectors is used for at least the first pacing pulse in the series. Otherpacing vectors may be used for subsequent pulses in the series of pacingpulses. Furthermore, additional pacing pulses may be generated in otherchambers of the heart, such as the right ventricle.

FIG. 2A illustrates a simplified block diagram of internal components ofthe IMD 100 (e.g., IMD) according to an embodiment. While a particularIMD 100 is shown, it is for illustration purposes only. One of skill inthe art could readily duplicate, eliminate, or disable the appropriatecircuitry in any desired combination to provide a device capable oftreating the appropriate chamber(s) with cardioversion, defibrillation,and pacing stimulation. The housing/CAN 140 for IMD 100, shownschematically in FIG. 2A may be programmably selected to act as theanode for at least some unipolar modes. The CAN 140 may further be usedas a return electrode alone or in combination with one or more of thecoil electrodes 128, 136, and 138 (all shown in FIG. 1) for shockingpurposes.

The IMD 100 further includes a connector (not shown) having a pluralityof terminals, 142, 143, 144 ₁-144 ₄, 146, 148, 152, 154, 156, and 158(shown schematically and, for convenience, with the names of theelectrodes to which they are connected). As such, to achieve rightatrial (RA) sensing and pacing, the connector includes at least an RAtip terminal (AR TIP) 142 adapted for connection to the atrial tipelectrode 122 (shown in FIG. 1) and an RA ring (AR RING) electrode 143adapted for connection to the RA ring electrode 123 (shown in FIG. 1).To achieve left chamber sensing, pacing, and shocking, the connectorincludes an LV tip terminal 144 ₁ adapted for connection to the D1electrode and additional LV electrode terminals 1442, 1443, and 144 ₄adapted for connection to the M2, M3, and P4 electrodes, respectively,of the Quadripolar LV lead 124 (shown in FIG. 1). The connector alsoincludes an LA ring terminal (A_(L) RING) 146 and an LA shockingterminal (A_(L) COIL) 148, which are adapted for connection to the LAring electrode 127 (shown in FIG. 1) and the LA coil electrode 128(shown in FIG. 1), respectively. To support right chamber sensing,pacing, and shocking, the connector further includes an RV tip terminal(V_(R) TIP) 152, an RV ring terminal (V_(R) RING) 154, an RV coilterminal (RV COIL) 156, and an SVC coil terminal (SVC COIL) 158, whichare adapted for connection to the RV tip electrode 132, the RV ringelectrode 134, the RV coil electrode 136, and the SVC coil electrode 138(all four electrodes shown in FIG. 1), respectively.

At the core of the IMD 100 is a programmable microcontroller 160, whichcontrols the various modes of stimulation therapy. The microcontroller160 (also referred to herein as a control unit or controller) includes amicroprocessor or equivalent control circuitry, designed specificallyfor controlling the delivery of stimulation therapy. The microcontroller160 may further include RAM or ROM memory, logic and timing circuitry,state machine circuitry, and/or I/O circuitry. The microcontroller 160includes the ability to process or monitor input signals (data) ascontrolled by a program code stored in a designated block of memory. Thedetails of the design and operation of the microcontroller 160 are notcritical to the invention. Rather, any suitable microcontroller 160 maybe used that carries out the functions described herein. Among otherthings, the microcontroller 160 receives, processes, and manages storageof digitized cardiac data sets from the various sensors and electrodes.

A pulse generator 170 and a pulse generator 172 are configured togenerate and deliver a pacing pulse from at least one RV or RA pacingsite, such as at one or more pacing sites along the RA lead 120, the RVlead 130, and/or the LV lead 124 (all three leads shown in FIG. 1). Forexample, the pulse generator 170 generates pulses for delivery by the RAlead 120 and/or RV lead 130, while the pulse generator 172 generatespulses for delivery by the LV lead 124. The pacing pulses are routedfrom the pulse generators 170, 172 to selected electrodes within theleads 120, 124, 130 through an electrode configuration switch 174. It isunderstood that in order to provide stimulation therapy in each of thefour chambers of the heart, the pulse generators 170 and 172, mayinclude dedicated, independent pulse generators, multiplexed pulsegenerators, or shared pulse generators. The pulse generators 170, 172are controlled by the microcontroller 160 via appropriate controlsignals 176, 178, respectively, to trigger or inhibit the stimulationpulses, including the timing and output of the pulses.

The pulse generators 170, 172 deliver, in connection with measuring thebase capture threshold, successive stimulation pulses that havedifferent stimulation amplitudes starting at an upper limit of the outertest range and decreasing by predetermined amounts. The pulse generators170, 172 deliver, in connection with measuring the secondary capturethreshold, one or more pacing pulses having stimulation amplitudes thatvary over the inner test range.

Optionally, the pulse generators 170, 172 deliver one or more pacingpulses beginning with an initial stimulation amplitude having a voltagethat is lower than a voltage of an initial stimulation amplitudeassociated with the outer test range used to measure the base capturethreshold. The pulse generators 170, 172, in connection with measuringthe base and secondary capture thresholds, begin at first and secondouter voltages corresponding to one of the limits of the outer and innertest ranges, respectively, the first and second outer voltages differingfrom one another.

The electrode configuration switch 174 may include a plurality ofswitches for connecting the desired electrodes to the appropriate I/Ocircuits, thereby providing complete electrode programmability.Accordingly, the switch 174, in response to a control signal 180 fromthe microcontroller 160, controls the polarity of the stimulation pulses(e.g., unipolar, bipolar, etc.) by selectively actuating the appropriatecombination of switches (not shown) as is known in the art. The switch174 also switches among the various LV electrodes 126 to select thechannels (e.g., vectors) to deliver and/or sense one or more of thepacing pulses. As explained herein, the switch 174 couples multiple LVelectrode terminals 144 ₁-144 ₄ correspond to cathodes when connected tothe pulse generator 172.

Atrial sensors or sensing circuits 182 and ventricular sensors orsensing circuits 184 may also be selectively coupled to the RA lead 120,the LV lead 124, and/or the RV lead 130 (all three leads shown inFIG. 1) through the switch 174. The atrial and ventricular sensors 182and 184 have the ability to detect the presence of cardiac activity ineach of the four chambers of the heart 105 (shown in FIG. 1). Forexample, the ventricular sensor 184 is configured to sense LV activationevents at multiple LV sensing sites, where the activation events aregenerated in response to a pacing pulse or an intrinsic event. In anembodiment, the ventricular sensor 184 senses along at least foursensing vectors, each sensing vector utilizing a sensing electrode inthe left ventricle.

The atrial sensing circuits 182 and ventricular sensing circuits 184 mayinclude dedicated sense amplifiers, multiplexed amplifiers, or sharedamplifiers. The switch 174 determines the “sensing polarity” or sensingvector of the cardiac signal by selectively opening and/or closing theappropriate switches, as is known in the art. In this way, a clinicianmay program the sensing polarity independent of the stimulationpolarity. The outputs of the atrial and ventricular sensing circuits 182and 184 are connected to the microcontroller 160. The outputs, in turn,are able to trigger or inhibit the atrial and ventricular pulsegenerators 170 and 172, respectively, in a demand fashion in response tothe absence or presence of cardiac activity in the appropriate chambersof the heart 105.

Cardiac signals are also applied to the inputs of an analog-to-digital(A/D) data acquisition system 190. The A/D data acquisition system 190is configured to acquire intracardiac electrogram (IEGM) signals,convert the raw analog data into a digital signal, and store the digitalsignals for later processing and/or telemetric transmission. Thetelemetric transmission may be to an external programmer 104, a bedsidemonitor, and/or a personal advisory module (PAM) 102. The dataacquisition system 190 may be operatively coupled to the RA lead 120,the LV lead 124, and the RV lead 130 (all three leads shown in FIG. 1)through the switch 174 to sample cardiac signals across any pair ofdesired electrodes.

The microcontroller 160 includes timing control module 161 to controlthe timing of the stimulation pacing pulses, including, but not limitedto, pacing rate, atrio-ventricular delay, interatrial conduction delay,interventricular conduction delay, and/or intraventricular delay. Thetiming control module 161 can also keep track of the timing ofrefractory periods, blanking intervals, noise detection windows, evokedresponse detection windows, alert intervals, marker channel timing,etc., which is known in the art.

The microcontroller 160 further includes an arrhythmia detector 162 foroperating the system 100 as an implantable cardioverter/defibrillatordevice. The detector 162 determines desirable times to administervarious therapies. For example, the detector 162 may detect theoccurrence of an arrhythmia and automatically control the application ofan appropriate electrical shock therapy to the heart aimed atterminating the detected arrhythmia. To this end, the microcontroller160 further controls a shocking circuit 173 by way of a control signal179. The shocking circuit 173 generates shocking pulses that are appliedto the heart of the patient through at least two shocking electrodes.The shocking pulses may be selected from the LA coil electrode 128, theRV coil electrode 136, and/or the SVC coil electrode 138 (all threeelectrodes shown in FIG. 1). The CAN 140 may act as an active electrodein combination with the RV coil electrode 136, or as part of a splitelectrical vector using the SVC coil electrode 138 or the LA coilelectrode 128 (e.g., with the RV coil electrode 136 as a commonelectrode).

The microcontroller 160 may additionally include a morphology detector164. The arrhythmia detector 162 and/or morphology detector 164 may beimplemented in hardware as part of the microcontroller 160, or assoftware/firmware instructions programmed into the system 100 andexecuted on the microcontroller 160 during certain modes of operation.

The microcontroller 160 controls the actual delivery of CRT pacingpulses to synchronize the contractions of the right and left ventricles.The microcontroller 160 controls the number, timing, and output of theCRT pacing pulses delivered during each cardiac cycle, as well as overwhich pacing vectors the pacing pulses are to be delivered. Themicrocontroller 160 also selects the sensing channels over which theresponses to the pulses are detected. The sensing channels or vectorsare associated with corresponding pacing vectors. Immediately afterpacing, the electrodes at the LV sensing sites that define the selectedsensing channels monitor the LV tissue for a sensed activation event.

The microcontroller 160 further includes a capture detection module 163.The capture detection module 163 may aid in acquisition, analysis, etc.,of data streams relating to evoked responses sensed at various LVsensing sites along corresponding sensing channels. In particular, thecapture detection module 163 may act to distinguish capture versusnon-capture versus undesired fusion of pacing pulses delivered alongcorresponding pacing vectors. The capture detection module 163determines capture thresholds of individual pacing vectors associatedwith one or more LV sensing sites. The microcontroller 160 and capturedetection module 163 operate as described herein to narrow test rangesused when search for capture thresholds for secondary pacing vectorsbased on previously determined capture thresholds for other pacingvectors. The operation of the microcontroller 160 and capture detectionmodule 163, as used in connection with determining capture thresholds,as described in more detail below in connection with FIGS. 4A-4C. Thecapture threshold may be used by the microcontroller 160 to determinethe LVEC pacing site and the pacing vector at the LVEC pacing site alongwhich to deliver LV pacing pulses, as described further below.

The pulse generator 170, 172 deliver a pacing sequence from the LVelectrode combination designated for the first LVEC pacing site. Thepulse generator 170, 172 deliver a first LV pacing pulse in the pacingsequence from the LV electrode combination. As noted herein, the LVelectrode combination includes an adjacent pair of LV electrodes. Thepulse generator 170, 172 is coupled to the switch 174 that sets theadjacent pair of LV electrodes as cathodes when delivering the LV pacingpulse. Optionally, the pulse generator 170, 172 and switch 174,controlled by the site designation module 169 designate adjacent atleast first and second LV electrodes as cathodes to simultaneouslydeliver at least a first pacing pulse.

Depending upon the implementation, the aforementioned components of themicrocontroller 160 may be implemented in hardware as part of themicrocontroller 160, or as software/firmware instructions programmedinto the device and executed on the microcontroller 160 during certainmodes of operation. In addition, the modules may be separate softwaremodules or combined to permit a single module to perform multiplefunctions. In addition, although shown as being components of themicrocontroller 160, some or all of the components/modules describedabove may be implemented separately from the microcontroller 160 usingapplication specific integrated circuits (ASICs) or the like.

The microcontroller 160 is further coupled to a memory 194 by a suitabledata/address bus 196. The programmable operating parameters used by themicrocontroller 160 are stored in the memory 194 and modified, asrequired, in order to customize the operation of IMD 100 to suit theneeds of a particular patient. Such operating parameters define, forexample, the amplitude or magnitude of the generated pacing pulses, waveshape, pulse duration, and/or vector (e.g., including electrodepolarity) for the pacing pulses. Other pacing parameters may includebase rate, rest rate, and/or circadian base rate. The memory 194 alsomay be utilized to store, at least temporarily, determinedcharacteristics about one or more pacing vectors, such as capturethresholds and the presence or absence of phrenic nerve stimulation(PNS), which is a potential side effect. The memory 194 stores one ormore correlation maps that are used to narrow test ranges when searchingfor capture thresholds.

FIG. 2B illustrates examples of correlation maps that may be stored inthe memory 194. The correlation maps 210 may include separate sets220-222 of maps, where each set 220-222 is related to a particularcombination of a base pacing vector and one or more secondary pacingvectors that are known to have a relation with the base pacing vector.For example, set 220 includes maps 211-213, each of which relates to adifferent combination of a common base pacing vector and differentsecondary pacing vectors. For example, the map 211 may correspond to theD1-RV coil base pacing vector and the D1-M2 secondary pacing vector,while map 212 corresponds to the D1-RV coil base pacing vector and D1-P4secondary pacing vector. The set 221 may correspond to a different basepacing vector (e.g. M3-RV coil), while the set 222 corresponds to get adifferent base pacing vector.

FIG. 2B further illustrates examples of correlation functions. Forexample, the map 211 illustrates a graph plotting a linear functionwhere the capture threshold associated with the base pacing vectorsplotted along the horizontal axis, while an upper limit of an inner testrange associated with the secondary pacing vector is plotted along thevertical axis. In the example of FIG. 2B, when the capture threshold ofthe base pacing vector is identified to be 2 V, the upper limit of theinner test range associated with the secondary pacing vector may be setto 4 V. In the foregoing example, the secondary pacing vector would betested for capture thresholds beginning at 4 V and then decreasing thepast value by a predetermined amount during each successive stimulationpulse. The maps 212 and 213 may Include the same linear correlationfunction or different correlation functions.

The set 221 illustrates an example of an alternative type of correlationfunction that may be used to define the relation between the capturethreshold for the base pacing vector and the upper limit of the innertest range for the secondary pacing vector. For example, the correlationfunction may represent a stepped function where the upper limit of theinner test range is progressively increased by stepped values as thecapture threshold of the base pacing vector increases.

As yet another example, the map 225 illustrates examples of simplemathematical formula that may be used to define the relation. Forexample, the formula may be one or more of Y=X*M and/or Y=X+M, where theX variable corresponds to the capture threshold of the base pacingvector and be Y variable corresponds to the upper limit of the innertest range and the constant M corresponds to a predetermined offsetprogrammed by a physician or automatically set based on pastexperiences. The correlation maps may be defined in various manners. Forexample, physician may program the correlation map. Alternatively, thesystem may automatically generate correlation maps based upon priorpatients or based upon past experience with an individual patient. Asanother example, correlation maps may be preprogrammed based on historicpatient the data for a large population of patients. As one example,patient data related to a large population of patients were analyzed (asdescribed below in more detail in connection with FIG. 3A-3C) toidentify relationships between capture thresholds associated withparticular combinations of pacing vectors. The relationships may then beused to define correlation maps to be programmed into the memory 194.

Returning to FIG. 2A, optionally, the operating parameters of theimplantable IMD 100 may be non-invasively programmed into the memory 194through a telemetry circuit 101 in telemetric communication with anexternal programmer device 104 or a bedside monitor 102, such as aprogrammer, trans-telephonic transceiver, or a diagnostic systemanalyzer. The telemetry circuit 101 is activated by the microcontroller160 through a control signal 106. The telemetry circuit 101 may allowIEGMs and status information relating to the operation of IMD 100(contained in the microcontroller 160 or the memory 194) to be sent tothe external device 102, and vice-versa, through an establishedcommunication link 103. An internal warning device 121 may be providedfor generating perceptible warning signals to a patient and/or caregivervia vibration, voltage, or other methods.

IMD 100 further includes an accelerometer or other physiologic sensor108. The physiologic sensor 108 is commonly referred to as a“rate-responsive” sensor because it may be used to adjust the pacingstimulation rate according to the exercise state (e.g., heart rate) ofthe patient. However, the physiological sensor 108 may further be usedto detect changes in cardiac output, changes in the physiologicalcondition of the heart, and/or diurnal changes in activity (e.g.,detecting sleep and wake states and arousal from sleep). Accordingly,the microcontroller 160 may respond to such changes by adjusting thevarious pacing parameters (such as rate, interatrial delay,interventricular delay, etc.) at which the atrial and ventricular pulsegenerators 170 and 172 generate stimulation pulses. While shown as beingincluded within IMD 100, it is to be understood that the physiologicsensor 108 may also be external to the IMD 100. Optionally, thephysiologic sensor 108 may still be implanted within or carried by thepatient. A common type of rate responsive sensor 108 is an activitysensor incorporating an accelerometer or a piezoelectric crystal, whichis mounted within the housing/case 140 of IMD 100. Other types ofphysiologic sensors 108 are also known, such as sensors that sense theoxygen content of blood, respiration rate and/or minute ventilation, pHof blood, ventricular gradient, stroke volume, cardiac output,contractility, and the like.

The IMD 100 additionally includes a battery 110, which providesoperating power to all of the circuits shown in FIG. 2. The makeup ofthe battery 110 may vary depending on the capabilities of IMD 100. Ifthe system only provides low voltage therapy (e.g., for repetitivepacing pulses), a lithium iodine or lithium copper fluoride cell may beutilized. For a IMD that employs shocking therapy, the battery may beconfigured to be capable of operating at low current drains for longperiods and then providing high-current pulses (for capacitor charging)when the patient requires a shock pulse. The battery 110 may also beconfigured to have a predictable discharge characteristic so thatelective replacement time can be detected.

As further shown in FIG. 2A, the IMD 100 has an impedance measuringcircuit 112, which is enabled by the microcontroller 160 via a controlsignal 115. Uses for an impedance measuring circuit 112 include, but arenot limited to, lead impedance surveillance during the acute and chronicphases for proper lead positioning or dislodgement; detecting operableelectrodes and automatically switching to an operable pair ifdislodgement occurs; measuring respiration or minute ventilation;measuring thoracic impedance for determining shock thresholds; detectingwhen the device has been implanted; measuring respiration; and detectingthe opening of heart valves, etc. The impedance measuring circuit 112 iscoupled to the switch 174 so that any desired electrode may be used.

The above described implantable medical device 100 was described as anexemplary IMD. One of ordinary skill in the art would understand thatone or more embodiments herein may be used with alternative types ofimplantable devices. Accordingly, embodiments should not be limited tousing only the above described device 100.

FIGS. 3A-3C illustrate data collected from studies using QuartetQuadripolar LV leads in accordance with embodiments herein. The data inFIGS. 3A-3C generally indicate that capture thresholds for a givencathode is often lowest when in the unipolar configuration (e.g., whenan RV coil electrode is used as an anode). Capture thresholds forbipolar vectors are generally higher than the capture thresholds for acorresponding unipolar vector (e.g. two times higher).

FIG. 3A illustrates LV capture thresholds collected for 354 patientsutilizing a quadrupole LV lead and a lead having an RV coil electrode inthe right ventricle. When measuring the capture thresholds, variouscombinations of electrodes were utilized, as denoted along thehorizontal axis. In particular, the electric combinations included theD1-RV coil electrode pair, M2-RV coil electrode pair, M3-RV coilelectrode pair, P4-RV coil electrode pair, D1-M2 electrode pair, D1-P4electrode pair, M2-P4 electrode pair, M3-M2 electrode pair, M3-P4electrode pair and the P4-M2 electrode pair. The vertical axisrepresents the voltage level associated with the capture threshold foreach patient. The data is organized in a box plot format where the dataassociated with each electrode pair is arranged in each bar 310, wherethe upper level 312 represents the third quartile (75%) of the data,while the lower level 314 represents the first quartile (25%). Theintermediate line 316 represents the median for the capture thresholdscollected in connection with the pacing vector defined by thecorresponding electrode pair. The additional markers 318 represent dataoutliers that are lower than the 1.5 interquartile range (IQR) of thefirst quartile, and higher than the 1.5 IRQ of the third quartile.

Upon inspecting the data in FIG. 3A, one characteristic that becomesapparent is that pacing vectors that utilize a unipolar configuration,for example when the RV coil represents the anode, exhibit lower capturethresholds, as compared to pacing vectors that utilize a bipolarconfiguration, in which the anode corresponds to an LV electrode. Forexample, the first and third quartiles of capture thresholds associatedwith the D1-RV coil electrode combination fall within a very small rangebetween 0.5 V and less than 2 V. Further, similarities in the first andthird quartiles of capture thresholds are clear when comparing the D1-RVcoil electrode combination with the D1-M2 and D1-P4 electrodecombinations, all of which use a common D1 electrode as the cathode. Asanother example, the first and third quartiles of the capture thresholdsare similar for the M2-RV coil electrode combination and M2-P4 electrodecombination, both of which use a common M2 electrode as the cathode. Asanother example, the first and third quartiles of the capture thresholdsare similar for the M3-RV coil electrode combination and the M3-M2electrode combination, both of which use the M3 electrode as thecathode.

In FIG. 3B, a collection of correlation plots are illustrated that mapcapture thresholds associated with different pacing vectors with thesame cathode electrode in accordance with embodiments herein. In theplots 320-327, the horizontal axis corresponds to the capture thresholdsmeasured in connection with one pacing vector, while the vertical axiscorresponds to the capture thresholds measured in connection withanother “related” pacing vector.

The pacing vectors along the horizontal axis may generally be referredto as “base” pacing vectors while the pacing vectors along the verticalaxis may be referred to as “secondary”. The terms base and secondary areused to indicate a relation between the pacing vectors. For example,when the capture threshold for a base pacing vector is measured, theinformation can be used to narrow the test range when searching for thecapture threshold of the secondary pacing vector.

A pacing vector may represent a secondary basing vector (e.g., plot 320D1-M2) relative to one pacing vector (e.g., D1-RVc). The same pacingvector may represent a base pacing vector (e.g., plot 322, D1-M2)relative to another pacing vector (D1-P4).

Each data point in an individual plots 320-327 corresponds to a pair ofcapture thresholds exhibited by an individual patient. The plots 320-327illustrates capture thresholds for combinations of pacing vectors thatutilize at least one LV electrode as a common cathode. For example, thedata in plot 320 shows a relation between capture thresholds (betweenzero and 10 V) associated with the pacing vector D1-RV coil (along thehorizontal axis) and the capture thresholds associated with pacingvector D1-M2 (along the horizontal axis). In the plot 320, the D1electrode represents the common cathode electrode.

The remaining plots 321-327 show correlation of capture thresholdbetween various other combinations of pacing vectors that utilize LVelectrodes as associated common cathodes. The plot 321 shows therelation between capture thresholds exhibited by a number of patientsfor the D1-P4 pacing vector and the D1-RV coil pacing vector, where theD1 electrode represents the common cathode. Plot 322 correlates capturethresholds associated with the D1-P4 pacing vector and D1-M2 pacingvector, where the D1 electrode represents the common cathode. The plots323-327 illustrate the following correlations: M2-P4 to M2-RV coil(where M2 is the common cathode); M3-M2 to M3-RV coil (where M3 is thecommon cathode); M3-P4 and M3-RV coil (where M3 is the common cathode);M3-P4 and M3-M2 (where M3 is the common cathode); and before—M2 andP4-RV coil (where P4 is the common cathode).

The plots 320-327 also include dividing lines 330-332 that separate eachof the plots 320-327 into four equal zones based select ratios R of thecapture thresholds. The ratio R=CAP1/CAP2, where CAP1 represents thecapture threshold associated with the “secondary” pacing vector denotedalong the vertical axis, while CAP2 represents the capture thresholdassociated with the “base” pacing vector denoted along the horizontalaxis. The dividing lines 330-332 define zones where R>2; 2>=R>1;1>=R>0.5; and 0.5>=R.

As illustrated in FIG. 3B, a substantial majority of the patientsexhibited capture thresholds associated with the pacing vectors plottedalong the vertical axis that fell within a factor of two (e.g. 2×) ofthe capture thresholds associated with the pacing vectors plotted alongthe horizontal axis. More specifically, over 95% of the patientsexhibited capture thresholds associated with bipolar pacingconfigurations (both electrodes on a common lead) that were within 2× ofthe capture thresholds associated with unipolar pacing configurations(electrodes are not on the same lead). For example, with reference tothe plot 320, approximately 1% of the patient population exhibited thecapture threshold associated with the D1-M2 pacing vector that wasgreater than two times the capture threshold associated with the D1-RVcoil pacing vector.

In the same plot 320, approximately 73% of the patients exhibitedcapture thresholds associated with the D1-M2 pacing vector that wasbetween one and two times the capture threshold associated with theD1-RV coil pacing vector. An additional 35% of the patients exhibited arelation between the capture thresholds associated with the pair ofpacing vectors where the ratio R was between 0.5 and 1.0, whileapproximate 1% of the patients exhibited a ratio between the capturethresholds of R less than 0.5. The remaining plots 321-327 also indicatethe percentages of the patient population that exhibited a ratio ofcapture thresholds between the corresponding pacing vectors. Forexample, the plot 324 illustrates that 1%, 73%, 23% and 3% of thepatient population fell within each of the corresponding zones, whilethe plot 326 illustrates that 6%, 23%, 70% and 1% of the patientpopulation fell within each of the corresponding zones.

The data illustrated in FIG. 3B indicates that the capture thresholdsassociated with unipolar configurations are lower than the capturethresholds associated with bipolar configurations. The differences inthe capture thresholds for unipolar configurations versus bipolarconfigurations that use a common cathode exhibit a somewhat predictableouter relation. For example, the outer relation in the data Illustratedin FIG. 3B represents a relationship of 2X (2 times).

FIG. 3C illustrates a series of histograms plotting differences betweencapture thresholds for the same patient data used to derive the graphsand plots in FIGS. 3A and 3B. The histograms 340-345 relate to differentselect combinations of electrodes and illustrate the differences betweencapture thresholds associated with bipolar pacing vectors and unipolarpacing vectors that utilize a common cathode. The histograms 340-345illustrate differences in voltage along the horizontal axis and thenumber of patients that exhibit the corresponding voltage differencealong the vertical axis.

More specifically, the histogram 340 illustrates in bar 350 that over200 patients exhibited a difference between −0.25 V and 0.25 V in thecapture thresholds associated with the D1-M2 electrode combination andthe D1-RV coil electrode combination. The bar 352 illustrates that lessthan 100 patients exhibited a difference between 0.25 V and 0.75 V,while even fewer patients exhibited a difference below −0.25 V orgreater than 0.75 V. In the histogram 343, the bar 353 illustrates thatover 100 patients exhibited a difference between −0.25 V and 0.25 Vbetween the capture thresholds associated with the M3-M2 electrodecombination and M3-RV coil electric combinations. The bar 354illustrates that approximately 100 patients exhibited a differencebetween 0.25 V and 0.75 V in connection with the capture thresholdsassociated with the M3-P4 electrode combination and M3-RV coil electrodecombination. The remaining histograms 341-342 and 344-345 illustratefurther relations between the differences in the corresponding electrodecombinations.

From the histograms 340-345, various information can be derived. Forexample, a very high percentage of the patients exhibited bipolarcapture thresholds within one volt above the unipolar capture thresholdwhen the D1 electrode was used as a common cathode between relatedbipolar and unipolar configurations. In addition, more than 90% of thepatients exhibited bipolar capture thresholds within 2 V above theunipolar capture threshold when the M2, M3 or P4 electrodes were used asthe common cathode between related bipolar and unipolar configurations.

As explained herein, methods and systems are described that utilize therelationships illustrated in the plots and charts of FIGS. 3A-3C inconnection with determining test ranges to use when searching forcapture thresholds associated with various pacing vectors.

FIG. 4A illustrates a method for automatically determining capturethresholds for various pacing vectors in accordance with embodimentsherein. At 402, the capture detection module 163 selects a base pacingvector and a base or outer test range. For example, the base pacingvector may be defined by a combination of electrodes that affords aunipolar configuration, such as the D1-RV coil electrode combination.When the D1-RV coil electrode combination is chosen, the RV coilelectrode is set as an anode, while the D1 electrode is set as thecathode. The base or outer test range corresponds to upper and lowerstimulation limits, and may be defined in various manners. The upper andlower stimulation limits correspond to a stimulation parameter relatedto an amount of stimulation amplitude that is delivered to the heart.For example, the stimulation limits may be defined based on voltagelevels, in which case the upper and lower limits may representpredetermined upper and lower voltages (e.g. 7.5 V and zero).

Optionally, the stimulation limits may correspond to another parameterthat defines stimulation pulses and stimulation amplitude, such as pulsewidth, a number of pulses, pulse shape and the like.

At 404, the capture detection module 163 performs one or more capturethreshold measurements until identifying a capture threshold associatedwith the base pacing vector. For example, a base capture threshold ismeasured for a base pacing vector that is defined by a first LVelectrode provided on the multi-pole LV lead and a second/referenceelectrode located remote from the LV chamber. For example, thesecond/reference electrode may represent an electrode in the RV, such asan RV tip electrode, RV coil electrode or RV ring electrodes.Optionally, the second/reference electrode may represent the CAN of theIMD. As another option, the second/reference electrode may be located inthe right atrium and/or proximate to the left atrium. An example ofoperations that may be carried out at 404 are described below in moredetail in connection with FIG. 4B. As explained below in connection withFIG. 4B, the measuring operation includes delivering a series of pacingpulses having different stimulation amplitudes that are varied over theouter test range, until losing capture.

At 406, the capture detection module 163 utilizes a correlation map toidentify an inner or secondary test range for a secondary pacing vector.For example, the secondary pacing vector represents a vector thatutilizes a cathode electrode that is common to the cathode electrodeutilized in the base pacing vector. The secondary pacing vector alsorepresents a vector that exhibits some level of correlation to the basepacing vector. For example, when the D1-RV coil electrode combination isused as the base pacing vector, the secondary pacing vector may beidentified to be the D1-M2 electrode combination or the D1-P4 electrodecombination (or another combination). The capture detection module 163determines the secondary or inner test range by using the capturethreshold measured at 404 as an input to the correlation map.

For example, one of the correlation maps illustrated in FIG. 2B may beused to Identify which combination of electrodes defines a secondarypacing vector known to have a relation with the present base pacingvector. The correlation maps from FIG. 2B may then also be used toidentify one or more outer limits of an inner test range to be used whensearching for the capture threshold associated with the secondary pacingvector. The correlation map may be defined in various manners and withvaried levels of complexity. For example, the correlation map mayrepresent a formula that defines the upper limit of the inner test rangeto be a factor of the capture threshold determined at 404 (e.g. 2*CAP1,where CAP1 represents the capture threshold measured at 404). As anotherexample, the correlation map may add a predetermined fixed voltage tothe capture threshold determined at 404 to obtain an upper limit of theinner test range (e.g., CAP1+2V). In the present example, thecorrelation map only defines the upper limit of the inner test range,while the lower limit of the inner test range remains the same as thelower limit of the outer test range.

Optionally, the correlation map may also define a lower limit for theinner test range that differs from the lower limit of the outer testrange. As one example, the upper and lower limits of the inner testrange may be defined as predetermined positive and negative multiples ofthe capture threshold determined at 404 (e.g. upper limit=CAP1*2 andlower limit=CAP1*(−1)). As another example, the upper and lower limitsof the inner test range may be defined by adding and subtractingpredetermined constants from the capture threshold determined at 404(e.g. upper limit=CAP1+3V and lower limit=CAP1−2V).

Optionally, the correlation map may represent a linear function thatmaps an input (corresponding to the capture threshold of the base pacingvector) to an output (corresponding to the capture threshold of thesecondary pacing vector). The linear function may have a nonzero slopesuch that, as the capture threshold for the base pacing vectorincreases, the output progressively increases to define higher upperlimits for the secondary test range. Optionally, the correlation map mayrepresent a non-linear function that maps inputs to outputs.

At 408, the capture detection module 163 measures the capture thresholdfor the secondary pacing vector utilizing one or more capture settingswithin the inner test range. An example of the operations that may becarried out at 408 are described below in more detail in connection withFIG. 4C. As explained below in connection with FIG. 4C, the measuringoperation delivers a series of pacing pulses having differentstimulation amplitudes that are varied over the inner test range, untilcapture is lost.

At 410, the process determines whether additional secondary pacingvectors exist that are associated with the current base pacing vectorand are to be tested. If so, flow returns to 406. Otherwise, flowadvances to 412. When the flow returns from 410 to 406, the operationsof 406 and 408 are repeated for the next secondary pacing vector (andassociated electrode combination).

At 412, the process determines whether additional base pacing vectorsare to be tested. If so, flow returns to 402 and the operations at402-410 are repeated. Otherwise, the process ends. With reference to thecharts illustrated in FIGS. 3A-3C, the operations at 406 and 408 may berepeated for the secondary pacing vectors D1-M2 and D1-P4 electrodecombinations utilizing corresponding inner test ranges as defined basedon the capture threshold determined for the D1-RV coil electrodecombination. Further, the operations at 402-412 may be repeated formultiple base pacing vectors, such as the D1-M2 electrode combination,the M2-RV coil electrode combination, the M3-RV coil electrodecombination, the M3-M2 electrode combination and the P4-RV coilelectrode combination.

FIG. 4B illustrates an example of the operations performed at 404 (FIG.4A) to measure the capture threshold associated with a base pacingvector. Beginning at 432, the capture detection module 163 sets thestimulation parameters to a first limit of the outer test range. Forexample, when the parameter of interest corresponds to voltage, theinitial stimulation pulse is set to deliver a pacing pulse with arelatively high pacing voltage (e.g. 7.5 V).

At 434, the capture detection module 163 delivers one or morestimulation pulses utilizing the stimulation parameters set at 432. At436, the capture detection module 163 collects/senses evoke responsesthat occur in response to the delivered stimulation pulses. At 438, thecapture detection module 163 analyzes the most recently collected evokeresponse to determine whether loss of capture has occurred. For example,the morphology or another characteristic of interest from the evokeresponse may be analyzed relative to one or more thresholds ortemplates. The threshold and template may be set to be representative ofan evoke response that indicates that the stimulation pulse achievedcapture of the heart tissue of Interest.

At 440, the capture detection module 163 determines whether capture hasbeen lost based on the evoke response from the most recent stimulationpulse. When capture is lost, flow advances to 446. Otherwise, flowcontinues to 442. At 442, the capture detection module 163 determineswhether the present stimulation limits correspond to an opposed secondlimit of the outer test range (e.g. the lowest stimulation voltage to beapplied, the shortest stimulation pulse to be utilized, etc.). When asecond limit is reached, flow moves from 442 to 446. Otherwise, flowcontinues to 444. At 444, the capture detection module 163 adjusts thecapture settings associated with one or more stimulation parameters by apredetermined incremental value. For example, the voltage associatedwith the stimulation pulse may be decreased by a predetermined amount.Additionally or alternatively, the pulse width number of pulses and thelike associated with the stimulation pulse may be decreased by apredetermined amount. Thereafter, flow returns to 434 and the operationsat 434 through 442 are repeated.

In accordance with at least one embodiment, the operations of FIG. 4Bare repeated, while measuring the base capture threshold, by deliveringa series of stimulation pulses where successive stimulation pulses havedifferent stimulation amplitudes starting at an upper limit of the outertest range and decreased by predetermined amounts.

The process of FIG. 4B is continuously repeated until either capture islost for the heart tissue of interest or the process steps through thecomplete outer test range for the stimulation parameter of interestwithout losing capture. When either condition occurs, flow moves to 446where the capture setting is saved as the capture threshold. Forexample, the capture threshold may represent the last stimulationvoltage that successfully achieved capture or, when capture is neverlost, the lowest stimulation voltage within the outer test range.

FIG. 4C illustrates an example of the operations performed at 408 (FIG.4A) to measure the capture threshold associated with a secondary pacingvector. Beginning at 462, the capture detection module 163 sets thestimulation parameters to a first limit of the inner test range. Forexample, when the parameter of interest corresponds to voltage, theinitial stimulation pulses set to deliver a pacing pulls with arelatively high pacing voltage (e.g. 7.5 V).

At 464, the capture detection module 163 delivers one or morestimulation pulses utilizing the stimulation parameters set at 462. At466, the capture detection module 163 collects evoke responses thatoccur in response to the stimulation pulses delivered. At 468, thecapture detection module 163 analyzes the most recently collected evokeresponse to determine whether loss of capture has occurred. For example,the morphology or another characteristic of interest from the evokeresponse may be analyzed relative to one or more thresholds ortemplates. The threshold and templates may be set to be representativeof evoke responses that indicate that the stimulation pulses achievedcapture of the heart tissue of interest.

At 470, the capture detection module 163 determines whether capture hasbeen lost based on the evoke response from the most recent stimulationpulse. When capture is lost, flow advances to 476. Otherwise, flowcontinues to 472. At 472, the capture detection module 163 determineswhether the present stimulation limits correspond to an opposed secondlimit of the inner test range (e.g. the lowest stimulation voltage to beapplied, the shortest stimulation pulse to be utilized, etc.). When asecond limit is reached, flow moves from 472 to 476. Otherwise, flowcontinues to 474. At 474, the capture detection module 163 adjusts thecapture settings associated with one or more stimulation parameters by apredetermined incremental value. For example, the voltage associatedwith the stimulation pulse may be decreased by a predetermined amount.Additionally or alternatively, the pulse width associated with thestimulation pulse may be decreased by a predetermined amount.Thereafter, flow returns to 464 and the operations at 464 through 472are repeated.

The process of FIG. 4C is continuously repeated until either capture islost for the part tissue of interest or the process steps through thecomplete inner test range for the stimulation parameter of interestwithout losing capture. When either condition occurs, flow moves to 476where the capture setting is saved as the capture threshold. Forexample, the capture threshold may represent the last stimulationvoltage that successfully achieved capture or, when capture is neverlost, the lowest stimulation voltage within the inner test range.

FIG. 4D illustrates a “quick scan” or “abbreviated scan” method forautomatically determining capture thresholds for various pacing vectorsin accordance with embodiments herein. For example, the quick scanmethod may limit the determination of capture thresholds to a subset ofthe available outer test range (e.g. utilizing an upper cut-offstimulation amplitude of 2 V or otherwise). As another example, thequick scan method may limit the determination of capture thresholds to asubset of the available inner test range. The quick scan methodidentifies vectors with thresholds below the cut-off in a relativelyquick manner. For example, physicians may choose to only consider LVvectors with thresholds below a certain cut-off stimulation amplitude(e.g. 2 V). When a physician is interested only in a limited range ofcut-off stimulation amplitudes, the capture threshold test describedherein may be configured to immediately start with the desired cut-offstimulation amplitude. When loss of capture is detected at the desiredcut-off stimulation amplitude, the process proceeds to the next base orsecondary vector without determining the capture threshold associatedwith the present vector. When a capture threshold is detected, theprocess continues to decrement the test stimulation amplitude until lossof capture is determined. The quick scan method may be applied inconnection with measuring the capture thresholds for base pacing vectorsand/or for secondary pacing vectors.

At 482, the capture detection module 163 selects a base pacing vectorand a base or outer test range having an abbreviated cut-off stimulationamplitude (e.g 2 V and the like). As explained herein, the base pacingvector may be defined by a combination of electrodes that affords aunipolar configuration, such as the D1-RV coil electrode combination.The base or outer test range corresponds to an abbreviated upperstimulation limit and a lower stimulation limits, which may be definedin various manners.

At 484, the capture detection module 163 determines whether loss ofcapture occurred at the cut-off stimulation amplitude. When loss ofcapture is detected, flow returns to 482 where a new base pacing vectoris selected. When loss of capture occurs at the cut-off stimulationamplitude associated with a base pacing vector, during the abbreviatedscan, no further capture threshold testing is performed in connectionwith the associated base pacing vector. Instead, the process moves on toone or more other base pacing vectors of potential interest.

Alternatively, at 484, when the capture detection module 163 determinesthat a capture threshold was measured at the cut-off stimulationamplitude, flow advances to 486. At 486, the capture detection module163 performs one or more additional capture threshold measurements untilidentifying a capture threshold associated with the base pacing vector.An example of operations that may be carded out, at 484, are describedin connection with FIG. 4B. The measuring operation includes deliveringa series of pacing pulses having different stimulation amplitudes thatare varied over the test range, until losing capture.

At 488, the capture detection module 163 utilizes a correlation map toidentify an inner or secondary test range for a secondary pacing vector.For example, the secondary pacing vector represents a vector thatutilizes a cathode electrode that is common to the cathode electrodeutilized in the base pacing vector. The secondary pacing vector alsorepresents a vector that exhibits some level of correlation to the basepacing vector. For example, one of the correlation maps illustrated inFIG. 2B may be used to identify which combination of electrodes definesa secondary pacing vector known to have a relation with the present basepacing vector.

At 490, the capture detection module 163 measures the capture thresholdfor the secondary pacing vector utilizing one or more capture settingswithin the inner test range. An example of the operations that may becarried out at 490 are described in more detail in connection with FIG.4C. As explained below in connection with FIG. 4C, the measuringoperation delivers a series of pacing pulses having differentstimulation amplitudes that are varied over the inner test range, untilcapture is lost.

Optionally, at 490, the capture detection module 163 may perform anabbreviated capture threshold test in connection with the secondarypacing vector. For example, an initial capture threshold test may beapplied at the secondary pacing vector utilizing the upper limit of theinner test range. At 490, the capture detection module 163 may determinewhether loss of capture occurred at the upper limit of the inner testrange for the present secondary pacing vector. When loss of capture isdetected, the present secondary pacing vector is not further tested fora capture threshold. Instead, flow advances to 492 and the presentsecondary pacing vector is disregarded.

At 492, the process determines whether additional secondary pacingvectors exist that are associated with the current base pacing vectorand are to be tested. If so, flow returns to 488. Otherwise, flowadvances to 494. When the flow returns from 492 to 488, the operationsof 488 and 490 are repeated for the next secondary pacing vector. At494, the process determines whether additional base pacing vectors areto be tested. If so, flow returns to 482 and the operations of FIG. 4Dare repeated. Otherwise, the process ends.

Optionally, the abbreviated or quick scan process described inconnection with FIG. 4D may be performed in connection with some or allbase pacing vectors and/or only in connection with some or all secondarypacing vectors.

FIG. 5 illustrates a functional block diagram of an external device 600that is operated in accordance with the processes described herein andto interface with the implantable medical device 100 as shown in FIGS. 1and 2 and described herein. The external device 600 may be the externalprogrammer device 104 shown in FIG. 2. The external device 600 may takethe form of a workstation, a portable computer, an IMD programmer, aPDA, a cell phone, and the like. The external device 600 includes aninternal bus that connects/interfaces with a Central Processing Unit(CPU) 602, ROM 604, RAM 606, a hard drive 608, a speaker 610, a printer612, a CD-ROM drive 614, a floppy drive 616, a parallel I/O circuit 618,a serial I/O circuit 620, a display 622, a touch screen 624, a standardkeyboard 626, custom keys 628, and/or a telemetry subsystem 630. Theinternal bus is an address/data bus that transfers information betweenthe various components described herein. The hard drive 608 may storeoperational programs as well as data, such as waveform templates,determinations on presence of PNS at various electrode locations, and/orcapture thresholds for pacing vectors.

The CPU 602 includes a microprocessor, a micro-controller, and/orequivalent control circuitry, designed specifically to controlinterfacing with the external device 600 and with the IMD 100. The CPU602 may include RAM or ROM memory, logic and timing circuitry, statemachine circuitry, and/or I/O circuitry to interface with the IMD 100.The ROM 604, RAM 606 and/or hard drive 608 store program instructionsthat one executed by one or more processors (e.g., the CPU 602) toperform the operations described herein.

The display 622 may be connected to a video display 632. The display 622displays various forms of information related to the processes describedherein. The touch screen 624 may display graphic user informationrelating to the IMD 100. The touch screen 624 accepts a user's touchinput 634 when selections are made. The keyboard 626 (e.g., a typewriterkeyboard 636) allows a user to enter data to displayed fields, as wellas interface with the telemetry subsystem 630. Furthermore, custom keys628 turn on/off 638 (e.g., EVVI) the external device 600. The printer612 prints copies of reports 640 for a physician to review or to beplaced in a patient file, and speaker 610 provides an audible warning(e.g., sounds and tones 642) to the user. The parallel I/O circuit 618interfaces with a parallel port 644. The serial I/O circuit 620interfaces with a serial port 646. The floppy drive 616 acceptsdiskettes 648. Optionally, the floppy drive 616 may include a USB portor other interface capable of communicating with a USB device such as aflash memory stick. The CD-ROM drive 614 accepts CD ROMs 650. The CD-ROMdrive 614 optionally may include a DVD port capable of reading and/orwriting DVDs.

The telemetry subsystem 630 includes a central processing unit (CPU) 652in electrical communication with a telemetry circuit 654, whichcommunicates with both an IEGM circuit 656 and an analog out circuit658. The IEGM circuit 656 may be connected to leads 660. The IEGMcircuit 656 is also connected to the implantable leads 120, 124 and 130(shown in FIG. 1) to receive and process IEGM cardiac signals.Optionally, the IEGM cardiac signals sensed by the leads 120, 124 and130 may be collected by the IMD 100 and then wirelessly transmitted tothe telemetry subsystem 630 input of the external device 600.

The telemetry circuit 654 is connected to a telemetry wand 662. Theanalog out circuit 658 includes communication circuits to communicatewith analog outputs 664. The external device 600 may wirelesslycommunicate with the IMD 100 and utilize protocols, such as Bluetooth,GSM, infrared wireless LANs, HIPERLAN, 3G, 4G, satellite, as well ascircuit and packet data protocols, and the like. Alternatively, ahard-wired connection may be used to connect the external device 600 tothe IMD 100.

CLOSING

The block diagrams of embodiments herein illustrate various blocks thatmay be labeled “module”, “unit” and the like. It is to be understoodthat the modules, units, etc. represent circuits that may be implementedas hardware with associated instructions (e.g., software stored on atangible and non-transitory computer readable storage medium, such as acomputer hard drive, ROM, RAM, or the like) that perform the operationsdescribed herein. The hardware may include state machine circuitryhard-wired to perform the functions described herein. Optionally, thehardware may include electronic circuits that include and/or areconnected to one or more logic-based devices, such as microprocessors,processors, controllers, or the like. Optionally, the modules, units,etc. may represent processing circuitry such as one or more fieldprogrammable gate array (FPGA), application specific integrated circuit(ASIC), or microprocessor. The modules, units, etc. in variousembodiments may be configured to execute one or more algorithms toperform functions described herein. The one or more algorithms mayinclude aspects of embodiments disclosed herein, whether or notexpressly Identified in a flowchart or a method.

The various methods as illustrated in the FIGS and described hereinrepresent exemplary embodiments of methods. The methods may beimplemented in software, hardware, or a combination thereof. In variousof the methods, the order of the steps may be changed, and variouselements may be added, reordered, combined, omitted, modified, etc.Various of the steps may be performed automatically (e.g., without beingdirectly prompted by user input) and/or programmatically (e.g.,according to program instructions).

Various modifications and changes may be made as would be obvious to aperson skilled in the art having the benefit of this disclosure. It isintended to embrace all such modifications and changes and, accordingly,the above description is to be regarded in an illustrative rather than arestrictive sense.

The environment can include a variety of data stores and other memoryand storage media as discussed above. These can reside in a variety oflocations, such as on a storage medium local to (and/or resident in) oneor more of the computers or remote from any or all of the computersacross the network. In a particular set of embodiments, the informationmay reside in a storage-area network (“SAN”) familiar to those skilledin the art. Similarly, any necessary files for performing the functionsattributed to the computers, servers or other network devices may bestored locally and/or remotely, as appropriate. Where a system includescomputerized devices, each such device can include hardware elementsthat may be electrically coupled via a bus, the elements including, forexample, at least one central processing unit (“CPU” or “processor”), atleast one input device (e.g., a mouse, keyboard, controller, touchscreen or keypad) and at least one output device (e.g., a displaydevice, printer or speaker). Such a system may also include one or morestorage devices, such as disk drives, optical storage devices andsolid-state storage devices such as random access memory (“RAM”) orread-only memory (“ROM”), as well as removable media devices, memorycards, flash cards, etc.

Such devices also can include a computer-readable storage media reader,a communications device (e.g., a modem, a network card (wireless orwired), an infrared communication device, etc.) and working memory asdescribed above. The computer-readable storage media reader can beconnected with, or configured to receive, a computer-readable storagemedium, representing remote, local, fixed and/or removable storagedevices as well as storage media for temporarily and/or more permanentlycontaining, storing, transmitting and retrieving computer-readableinformation. The system and various devices also typically will includea number of software applications, modules, services or other elementslocated within at least one working memory device, including anoperating system and application programs, such as a client applicationor web browser. It should be appreciated that alternate embodiments mayhave numerous variations from that described above. For example,customized hardware might also be used and/or particular elements mightbe implemented in hardware, software (including portable software, suchas applets) or both. Further, connection to other computing devices suchas network input/output devices may be employed.

Various embodiments may further include receiving, sending, or storinginstructions and/or data implemented in accordance with the foregoingdescription upon a computer-readable medium. Storage media and computerreadable media for containing code, or portions of code, can include anyappropriate media known or used in the art, including storage media andcommunication media, such as, but not limited to, volatile andnon-volatile, removable and non-removable media implemented in anymethod or technology for storage and/or transmission of Information suchas computer readable instructions, data structures, program modules orother data, including RAM, ROM, Electrically Erasable ProgrammableRead-Only Memory (“EEPROM”), flash memory or other memory technology,Compact Disc Read-Only Memory (“CD-ROM”), digital versatile disk (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices or any other medium whichcan be used to store the desired information and which can be accessedby the system device. Based on the disclosure and teachings providedherein, a person of ordinary skill in the art will appreciate other waysand/or methods to implement the various embodiments.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that various modifications and changes may be made thereuntowithout departing from the broader spirit and scope of the invention asset forth in the claims.

Other variations are within the spirit of the present disclosure. Thus,while the disclosed techniques are susceptible to various modificationsand alternative constructions, certain illustrated embodiments thereofare shown in the drawings and have been described above in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific form or forms disclosed, but on the contrary,the intention is to cover all modifications, alternative constructionsand equivalents falling within the spirit and scope of the invention, asdefined in the appended claims.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the disclosed embodiments (especially in thecontext of the following claims) are to be construed to cover both thesingular and the plural, unless otherwise indicated herein or clearlycontradicted by context. The terms “comprising,” “having,” “including”and “containing” are to be construed as open-ended terms (i.e., meaning“including, but not limited to,”) unless otherwise noted. The term“connected,” when unmodified and referring to physical connections, isto be construed as partly or wholly contained within, attached to orjoined together, even if there is something intervening. Recitation ofranges of values herein are merely intended to serve as a shorthandmethod of referring individually to each separate value falling withinthe range, unless otherwise indicated herein and each separate value isincorporated into the specification as if it were individually recitedherein. The use of the term “set” (e.g., “a set of items”) or “subset”unless otherwise noted or contradicted by context, is to be construed asa nonempty collection comprising one or more members. Further, unlessotherwise noted or contradicted by context, the term “subset” of acorresponding set does not necessarily denote a proper subset of thecorresponding set, but the subset and the corresponding set may beequal.

Operations of processes described herein can be performed in anysuitable order unless otherwise indicated herein or otherwise clearlycontradicted by context. Processes described herein (or variationsand/or combinations thereof) may be performed under the control of oneor more computer systems configured with executable instructions and maybe implemented as code (e.g., executable instructions, one or morecomputer programs or one or more applications) executing collectively onone or more processors, by hardware or combinations thereof. The codemay be stored on a computer-readable storage medium, for example, in theform of a computer program comprising a plurality of instructionsexecutable by one or more processors. The computer-readable storagemedium may be non-transitory.

Preferred embodiments of this disclosure are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate and the inventors intend for embodiments of the presentdisclosure to be practiced otherwise than as specifically describedherein. Accordingly, the scope of the present disclosure includes allmodifications and equivalents of the subject matter recited in theclaims appended hereto as permitted by applicable law. Moreover, anycombination of the above-described elements in all possible variationsthereof is encompassed by the scope of the present disclosure unlessotherwise indicated herein or otherwise clearly contradicted by context.

All references, including publications, patent applications and patents,cited herein are hereby incorporated by reference to the same extent asif each reference were individually and specifically indicated to beincorporated by reference and were set forth in its entirety herein.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope. While the dimensions, types ofmaterials and coatings described herein are Intended to define theparameters of the invention, they are by no means limiting and areexemplary embodiments. Many other embodiments will be apparent to thoseof skill in the art upon reviewing the above description. The scope ofthe invention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Moreover, in the following claims, theterms “first,” “second,” and “third,” etc. are used merely as labels,and are not intended to impose numerical requirements on their objects.Further, the limitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. § 112(f), unless and until such claim limitations expresslyuse the phrase “means for” followed by a statement of function void offurther structure.

What is claimed is:
 1. A system for automatically determining capturethresholds for an implantable medical device adapted to deliver cardiacstimulus pacing using a multi-pole left ventricular (L V) lead.comprising: at least one processor; a pulse generator coupled to themulti-pole L V lead, the pulse generator being adapted to deliver todeliver cardiac stimulus pacing to one or more electrode of themulti-pole LV lead; and a memory coupled to the at least one processor,wherein the memory stores program instructions, wherein the programinstructions are executable by the at least one processor to: measure abase capture threshold for a base pacing vector utilizing stimulationpulses delivered by the pulse generator varied over at least a portionof an outer capture threshold test range, the base pacing vector definedby a first LV electrode provided on the LV lead and a secondaryelectrode located remote from an LV chamber; designate a secondarypacing vector that includes the first LV electrode and a second LVelectrode provided on the LV lead; define an inner test range havinglimits based on the base capture threshold, wherein at least one of thelimits for the inner test range differs from a corresponding limit forthe outer test range; and measure a secondary capture thresholdassociated with the secondary pacing vector utilizing stimulation pulsesvaried over at least a portion of the inner test range.
 2. The system ofclaim 1, further comprising a pulse generator that delivers, inconnection with measuring the base capture threshold, successivestimulation pulses that have different stimulation amplitudes startingat an upper limit of the outer test range and decreasing bypredetermined amounts.
 3. The system of claim 1, further comprising apulse generator that delivers, in connection with measuring thesecondary capture threshold, one or more pacing pulses havingstimulation amplitudes varying over the inner test range.
 4. The systemof claim 3, wherein the pulse generator delivers one or more pacingpulses beginning with an initial stimulation amplitude having a voltagethat is lower than a voltage of an initial stimulation amplitudeassociated with the outer test range used to measure the base capturethreshold.
 5. The system of claim 3, wherein the pulse generator, inconnection with measuring the base and secondary capture thresholds,begins at first and second outer voltages corresponding to one of thelimits of the outer and inner test ranges, respectively, the first andsecond outer voltages differing from one another.
 6. The system of claim1, further comprising a correlation map defining a relation between thebase capture threshold and at least one outer limit of the inner testrange.
 7. The system of claim 1, wherein the second outer voltage is setto equal a predetermined multiple of the first outer voltage or to equala difference between the first outer voltage and a predetermined offset.8. The system of claim 1, further comprising a pulse generator and aswitch, the switch defining the base and secondary pacing vectors byconnecting the pulse generator to the first LV electrode in a mannerthat sets the first LV electrode as a cathode electrode, the switchconnecting the second electrode and the neighbor LV electrode as anodeelectrodes.
 9. The system of claim 1, further comprising a switch thatsets the base pacing vector to represent a unipolar pacing configurationand that sets the secondary pacing vector to represent a bipolar pacingconfiguration.